158 PALEONTOLOGY OF NEW YORK. 



Davidson* in the " dorsal " valve of the free species, Crania (Pseudocrania) 

 divaricata, McCoy. In tlie opposite valve of Pholidops these scars do not 

 appear, and the interior margin of the callosity is uninterrupted In certain 

 species, particularly those of large size which have been found as internal casts, 

 the whole muscular area of the ventral (?) valve appears to be occupied by the 

 scars of the anterior adductors (see Plate IV i, figs. 26, 36). The fact that in 

 these cases the other muscular and the parietal scars are not defined is probably 

 due to imperfect preservation. 



The substance of the shells of Pholidops is calcareous and apparently im- 

 punctate. On account of their extreme tenuity it has been impossible to make 

 satisfactory sections, but there appears by magnification of the surface no evi- 

 dence of punctation. Should an impunctate character be demonstrated it will 

 be another important respect in which Pholidops differs from Crania. 



This group of shells was noticed as early as 1820 by Schlotheim, who, by 

 the designation Patellites (P. antiquus of the Gotland Upper Silurian lime- 

 stone) implied its relationship to Patella. Sowerby, in 1839, essentially 

 coincided with this opinion in referring an English species to Patella (P. 

 implicata). Thereafter, until 1859, the American species were placed under the 

 genus Orbicula, a name which at that time had come to include a great variety 

 of heterogeneous brachiopods, now mainly referred to Crania and Orbiculoidea. 

 McCoy, however, in 1859, considered the English species congeneric with the 

 ScHizoTRETA of KuTORGA, and, not recognizing the priority of the latter name, 

 placed both in D'Orbigny's genus, Orbiculoidea. Salter, in 1859, and David- 

 son as late as 1866, referred P. implicata, Sowerby, to Crania, and though the 

 latter author in 1883 corrects this reference and recognizes the term Pholidops, 

 no modification was suggested of the figures given of the interior of this 

 species in the British Silurian Brachiopoda (pi. viii, figs. 15, 16 a), which are 

 radically incorrect in representing the valves with posterior marginal muscular 

 scars. In 1859, in a revised list of the fosfeils described in the first two volumes 

 of the Palaeontology of New York, the term Craniops was proposed for the 



* British Silurian Brachiopoda, pi. viii, figs. 11, 11 a, 12a. 



